With the increased emphasis on environmental matters, one area of attention is in remediation of contaminated vadose zone soil. Soil venting is an attractive in-situ method of extracting vapor from volatile and semivolatile petroleum hydrocarbons and removing adsorbed liquid hydrocarbons from the vadose zone. In this method air is drawn between soil particles to volatilize the contaminant and accelerate the evaporation rate of the adsorbed hydrocarbons, and is then vented to the surf ace through vent wells. The vapor may be treated at the surface by suitable means, such as activated charcoal, so as to be discharged in concentrations compatible with local guidelines.
In carrying out a soil venting process a wellbore is drilled in the zone of interest and a casing containing openings for the passage of air is installed. Typically, the casing includes a screened section for this purpose which extends for a substantial distance, in the order of 10-20 feet, along the length of the casing. When suction is drawn on the vent well to draw air from the surf ace down through the soil, the air tends to follow the shortest flow path, which is from the area immediately surrounding the wellbore to the upper portion of the screened section. Therefore, in order to treat soil outside of this area it is normally necessary to provide additional vent wells. To treat soil which is deeper than the normal flow path of the air it would be necessary to provide new casings having lower screened sections. These are costly procedures, however, and it would be highly desirable to be able to enlarge the scope of treatment without having to employ them.
It is therefore an object of the invention to be able to treat a larger area of soil by means of a vent well without requiring additional wells or drastic modifications to conventional soil venting procedures.